Stray Gas Migration – Fact vs Fiction
One of the more serious issues confronting state regulatory agencies, particularly in the Marcellus Shale play, has been addressing the question “can these shale gas wells create new pathways for gas to contaminate private water wells”. The concern is that once gas enters a water well it has a direct route into the dwelling via the water service line. This can create the potential for a life threatening explosion. While gas in water wells is not an uncommon problem in the Appalachian Basin, few problems can be linked to natural gas development and production. Perhaps nothing more falsely places the blame on the natural gas industry than the “flaming faucet” clips that have been placed in the public domain by groups and individuals against shale gas development. The Pennsylvania Department of Environmental Protection addressed potential stray gas from natural gas development several years ago by putting new casing and cementing standards and notification requirements into its Chapter 78 rules. These standards were put in place to minimize any potential for stray gas movement from shale gas wells. These requirements do so by ensuring multiple layers of competent steel and cement are used in well construction and ensure prompt action if stray gas is detected.
The irony is that gas migration has a history in the Appalachian Basin unrelated to shale gas development or the historic conventional gas industry. Records dating back to the 1700’s in Pennsylvania note instances of gas bubbling into creeks and springs throughout the region and in some cases the gas being ignited (usually intentionally) for the thrill of the show. Though not obvious at the time, these were some of the first noted cases in the New World of natural gas migration occurring from shallow gas bearing formations, including shallow coal seams. Later, as civilization advanced and water wells became the choice for onsite water supplies, the well bore or casing became a perfect conduit for moving gas from these shallow formations directly into the well itself.
The problem of gas buildups occurring in more modern Pennsylvania water wells is in part due to the Commonwealth’s lack of water well construction standards. Many are surprised that there are no state standards for properly casing and venting water wells, particularly in known shallow gas areas. This lack of standards has left many homeowners in harm’s way as improperly or non-vented water wells allow shallow gas to accumulate and subsequently move with the water into the dwelling where the water is used. Legislative bills, meant to remedy this lack of standards, come and go virtually every legislative session – unfortunately none has managed to be enacted to date.
In an effort to clear any misconceptions and misinformation about shale gas creating or aggravating the stray gas problem, a recent study was completed that clears the air (no pun intended) relative to shale gas and its non-role in gas migration issues. Researchers Fred Baldassare from Echelon Applied Geochemistry Consulting, Mark McCaffrey from Weatherford Laboratories and John Harper from the US Geological Survey looked at 67 private water wells in a five county area in northeastern Pennsylvania where active gas well development was being conducted. Their goal was to ascertain the source of thermogenic gas reportedly found in a number of water waters by a prior Duke University study. The Duke study concluded that the presence of the deep formation thermogenic gas in shallow water wells likely pointed to shale gas wells as the factor for creating the pathways for this deep gas to move towards the surface. However, this Baldassare et al study fingerprinted and looked at isotropic signatures of the thermogenic gas found in the water well samples. Their results showed a surprising number of water wells – 88 percent – contained thermogenic gas but they found that none of it was from the Marcellus formation. Their conclusion was that the deeper thermogenic gases migrated over geologic time into shallower formations and mixed with shallower thermogenic gases. Consequently, the presence of thermogenic gas in water wells should not create an automatic link to shale gas operations. The best option for homeowners when addressing stray gas concerns would be to evaluate the presence of shallow gas formations in their area and, where appropriate, utilize sound water well construction and venting practices to eliminate the potential for gas buildups to occur.